Add the ability to save to a file a SpherePack containing some Clumps.
Into SpherePack : now the toFile method writes a fifth column containing the clump number (-1 if the sphere isn't clumped). The fromFile method uses the new information to append clumped Spheres.
Into Shop : loadSpheresFromFile method is modified to read and return the fifth column. Old files with 4 columns are still compatible.
Into CapillaryTriaxialTest and CohesiveTriaxialTest : Shop::loadSpheresFromFile is sometimes used here, so remove the clumpId information to match the "BasicSphere" typedef.